The present invention relates to chair structures and, more specifically, to a chair made more comfortable to sit.
Among chairs presently used in offices and the like, there exist chairs of the type which is capable of bending an upper portion of its back rearwardly. Such a chair, which allows the backbone of a person sitting thereon to bend backwardly thereby refreshing the sitting person, is generally of a construction having a shaft for rotation mounted intermediate between upper part and lower part of the backrest portion to allow a back portion above the shaft for rotation to incline rearwardly about the shaft for rotation.
With such a conventional construction having a shaft for rotation intermediate between the upper and lower parts of the backrest portion, however, the radius of gyration with which the upper back portion is inclined rearwardly is small and, hence, the upper end side of the upper back portion largely leans rearwardly. Consequently, when the upper back portion thus constructed is inclined rearwardly, it cannot support the shoulders or parts therearound of the sitting person and, hence, this condition is substantially the same as the absence of the upper back portion, making the sitting person unstable. Further, the provision of the shaft for rotation intermediate between the upper and lower parts of the backrest portion raises a problem that the load of the sitting person is concentrated on the shaft for rotation because the backrest portion steeply bends about the shaft, thus making the sitting person feel uncomfortable or giving him or her a sense of incongruity or the like.
With a view to solving the aforementioned problems, the present invention intends to provide a chair which is capable of inclining its back portion rearwardly while offering improved comfortableness to sit.
With a view to solving the foregoing problems, the present invention provides a chair wherein a back portion located rearwardly of a seat portion is divided into an upper back portion and a lower back portion, at least the upper back portion being capable of inclining rearwardly, characterized in that a fulcrum for rearwardly inclining the upper back portion is located below a seating surface, the upper back portion being allowed to incline rearwardly about the fulcrum.
Since the fulcrum for rearwardly inclining the upper back portion is located below the seat portion, the upper back portion can be moved rearwardly while rearwardly inclining gently, whereby the shoulders and parts therearound of a person sitting on the chair can be contacted and supported by the upper end side of the upper back portion.
The angle of rearward inclination of the upper back portion may vary depending upon the build, posture or preference of the sitting person. In such a case, it is sufficient to provide a plurality of fulcrums for rearwardly inclining the upper back portion below the seating surface for the sitting person to select any one of the fulcrums so that switching of rearwardly inclining modes of the upper back portion can be made. With the chair thus constructed, the sitting person is capable of selecting a desired one of modes including, for example, a mode of rearwardly inclining the upper back portion largely and a mode of rearwardly inclining it with a smaller radius of gyration. Thus, the chair can be more suited to the preference and the like of a person sitting thereon.
Further, the chair may be constructed such that the seat portion or the like is moved in cooperation with the switching of rearwardly inclining modes of the upper back portion. With this construction, it is possible to select a desired mode including movement of the seat portion.
If the chair having the back portion divided into the upper back portion and the lower back portion is constructed to allow the upper back portion to incline rearwardly with the lower back portion being maintained at a predetermined angle, the chair allows the sitting person to bend his or her backbone backwardly thereby refreshing the sitting person.
In the case where the upper back portion is inclined rearwardly relative to the lower back portion, the distance between the upper back portion and the lower back portion changes. To absorb this change in the distance, it is preferred that an upholstery member be attached to a body contacting part of the back portion. The provision of such an upholstery member makes it possible not only to absorb changes in the distance between the upper back portion and the lower back portion but also to make the surface of the whole back portion smooth.